The invention relates to a process for the production of a ball joint connection between a sliding shoe and a cylinder piston of a piston engine, particularly an axial piston engine.
In axial piston engines of swash plate construction, the cylinder pistons which are movable in cylinder bores are supported on the sliding surface of a swash plate via a sliding shoe in each case. It is conventional to connect the cylinder pistons to the sliding shoes by means of a ball joint connection so as to ensure a flat seating of the sliding sole of the sliding shoes on the sliding surface of the swash plate in every inclined position of the swash plate.
When producing a ball joint connection it is generally conventional to insert the ball head formed on the sliding shoe or the cylinder piston into a rounded-off recess of the corresponding counter-piece, i.e. the cylinder piston and/or sliding shoe. The recess is rounded off as a hollow hemisphere only in a solid angle region of approx. 180xc2x0. A region in the shape of a hollow cylinder which ends at an opening adjoins this hemispherical region of the recess. The opening diameter at the opening of the recess corresponds to the diameter in the region of the equator plane of the semi-hollow ball-shaped region of the recess. When the sliding shoe and the cylinder piston are joined the ball head formed on one of the two components is introduced into the recess and anchored positively in the recess. This is necessary so that a corresponding tensile force is transferable via the ball joint connection during the suction stroke of the piston engine.
In a current process for connecting the ball head to the corresponding recess, the edge region surrounding the ball head in the region of the opening of the recess is beaded, e.g. by means of rolling, after the spherical ball head has been inserted. A process of this kind emerges from DE-OS 1 776 027 for example. In contrast it is known from DE-AS 21 32 252 that, in order to anchor the ball head of the sliding shoe in the recess of the cylinder piston, a locking ring is used which is supported against an inner surface of the recess. The above two processes are relatively complex and mass production is associated with relatively high production and assembly costs.
The plastic deformation of the cylinder piston in the edge region surrounding the dome-shaped recess is associated with drawbacks in that the piston is subjected to a special hardening, by nitriding and a heat treatment for example, in order to improve wear resistance. This hardening does, however, conflict with a subsequent plastic deformation so that the region surrounding the dome-shaped recess must be omitted from the heat treatment, which signifies considerable additional outlay. There is also the problem that the high compressive force required to deform the cylinder piston generally made of steel leads to an undesired co-deformation of the ball head of the sliding shoe which is made of a copper or bronze alloy to improve the sliding properties. In practice it is therefore necessary to design the sliding shoe in two parts with a sliding part made of a copper or bronze alloy and a steel ball inserted into it.
In any event an additional, complex working step is required for the beading. The insertion of a locking ring to lock the ball head increases the number of parts required for assembly and has not proved successful in practice because of the high assembly and production outlay.
From DE 42 14 765 A1 it is known to provide the ball head of the sliding shoes with a flattening which is angled off in respect of the longitudinal axis of the sliding shoes. After insertion of the ball head into the recess of the cylinder piston it is possible to tilt the ball head in the recess in such a way that it cannot be pulled out of the recess. This process does, however, have the disadvantage that the interface between the ball head of the sliding shoe and the recess of the cylinder piston in the region of the edges of the ball head is subject to increased wear. Furthermore, the bearing surface is considerably reduced by the flattening. In addition the swivel angle which the swash plate may assume with respect to the cylinder drum is considerably restricted. This process cannot be used in particular for axial piston engines with swash plates which can swivel in both swivel directions.
The object of the invention is therefore to provide a process for the production of a ball joint connection between a sliding shoe and a cylinder piston which permits efficient and economical mass production.
The object is achieved by both the features of claim 1 and the features of claim 4 or 12.
The solution according to Claim 1 is based on the finding that an economical joining of the ball joint may be achieved in that the edge region surrounding the recess is elastically deformed on joining and the ball head is pressed into the recess after the fashion of a snap-fastener.
Claims 2 and 3 relate to advantageous developments of the solution according to claim 1.
According to claim 2 it is advantageous that the elastic stress distribution on pressing the ball head into the dome-shaped recess is radially distributed as uniformly as possible. According to claim 3 the pressing of the ball head into the recess may be facilitated in that a liquid or gaseous pressure medium is applied to the recess via a bore provided in the sliding shoe or the cylinder piston. An elastic expansion of the edge region of the recess is achieved in this way. According to claim 1 the elastic deformation of the edge region surrounding the recess may also be promoted in that radial slits are provided in the edge region.
The solution according to claim 4 is based on the finding that the ball joint connection may also be produced simply and inexpensively in that the ball head is first formed with a flattening, in order to introduce the ball head into the undercut recess. After the ball head has been inserted it is plastically deformed. Unlike the beading known from the prior art, it is advantageous in this case when the ball head consists of a readily deformable material, e.g. a copper or bronze alloy, which is conventionally used to form the sliding shoes. It is also advantageous when the recess forming the die is made of a hardened material such as is conventionally used for cylinder pistons. A plastic deformation of the ball head is thus more satisfactorily suited to the given material properties than the beading of the edge region of the recess known from the prior art.
Claims 5 to 11 relate to advantageous developments of the solution according to claim 5.
According to claim 9 a longitudinal bore, to which a liquid or gaseous pressure medium is applied for the plastic deformation of the ball head, in order radially to displace the material of the ball head, may pass through the ball head.
Alternatively, however, the material may also be displaced by means of a caulking mandrel inserted into the longitudinal bore according to claim 10. In this case it is advantageous when according to claim 11 the longitudinal bore has an internal projection which may be co-formed when the ball head is deformed according to the development according to claim 8.
The solution according to claim 12 is based on the finding that an economical joining of the ball joint may be achieved in that the edge region surrounding the recess and/or the ball head is thermally deformed prior to joining, the ball head is inserted into the recess and the desired engaging connection is produced by means of temperature adjustment of the ball head and the edge region surrounding the recess.
Claim 13 relates to an advantageous development of the invention. The thermal deformation may be combined with an elastic deformation.